1. Field Of The Invention
This invention relates to an improved molding composition containing a polyvinylidene fluoride polymer reinforced by glass fibers which composition can be thermoplastically worked. This invention relates to a reinforced polyvinylidene fluoride molding composition which can be worked by thermoplastic forming techniques.
2. Discussion Of The Prior Art
It is known that polyvinylidene fluoride (PVDF) is increasingly used in chemical apparatus and chemical plant construction on account of its resistance to chemicals and its thermal stability. Also, the good mechanical characteristics of unreinforced PVDF qualify this material for such uses.
In spite of these very favorable characteristics, there are applications in which PVDF could be used, in which its mechanical strength, especially under high temperature exposure, needs to be further improved. An improvement of such characteristics, such as the modulus of elasticity or the thermal stability of shape, would also make possible the use of smaller quantities of this material in the same applications without loss of strength.
The ability of PVDF to withstand mechanical stresses at temperatures above 100.degree. C is insufficient for many applications, so that it is desirable to improve these characteristics in this regard as well.
It is also known to improve the mechanical characteristics of thermoplastics by incorporating fibrous materials into them, especially glass fibers. The incorporation of these reinforcing additives and the further working of the compositions reinforced by them is accomplished without difficulty in the case of the known thermoplastics. For example, compositions containing polyvinyl chloride, polyesters, polyamides and copolymers of ethylene and tetrafluorethylene (PTFE) are compatible with glass fibers and can be extruded or injection molded on known machinery together with glass fibers of any desired composition.
In contrast thereto, PVDF is incompatible with the glass fibers commonly used in plastic reinforcing under the thermal and mechanical conditions of thermoplastic incorporation and shaping. This manifests itself in the fact that, when regular commercial glass fibers are incorporated into into them in the extruders known for the purpose, more or less severe degradation of the PVDF takes place, depending on the composition of the glasses, with the formation of gaseous hydrogen fluoride, which can be harmful to the health; in the worst case, the degradation can result in the destruction of the extruding machine.
These disadvantages of the thermoplastic incorporation of glass fibers are encountered even when sized glass filaments are used, so that it has hitherto been impossible to determine the cause of such degradation.
Instead of incorporating glass fibers into compositions containing PVDF by extrusion, it has therefore been proposed to bind the PVDF compositions to glass fiber fabrics or mats at temperatures below the dangerous temperature range.
This can be accomplished by various bonding methods, such as flame bonding or compression. The PVDF can also be applied to the fabrics or mats in the form of a dispersion. The disadvantage of these methods is that they are very labor intensive, and the products obtained cannot be further worked thermoplastically into all kinds of shaped products.
The problem therefore existed of finding a fibrous material with which PVDF can be reinforced without encountering the above-mentioned disadvantages. The problem furthermore existed of finding reinforced PVDF compositions which can be further worked by thermoplastic shaping methods.
It is an object of this invention, therefore, to provide a polyvinylidene fluoride polymer composition which is reinforced with a fibrous composition which does not adversely effect the polyvinylidene fluoride when the same is thermoplastically formed into a desired shape. It is a further object of this invention, therefore, to provide a glass fiber reinforced polyvinylidene fluoride polymeric composition in which there is no adverse glass fiber-polyvinylidene fluoride polymer interaction. It is a further object of this invention, therefore, to provide a polyvinylidene fluoride glass fiber reinforced molding composition in which during formation of the mass into desired shape substantial quantities of gaseous hydrogen fluoride are not evolved. It is a further object of this invention to provide a polyvinylidene fluoride molding composition which can be worked at temperatures of up to 350.degree. C thermoplastically without degradation of the polymer. These and other objects of this invention will become apparent from the following description and claims.